1. Field of the Invention
The present invention relates to a device intended for use on the distal end of an actively implantable electrical conductor to prevent a helical anchoring element, projecting from the distal end of the conductor, from damaging the walls of the cavities during implantation of the conductor into body cavities, such as veins and the heart.
2. Description of the Prior Art
Implantable electrical conductors, i.e. electrode cables, intended for connection at their proximal end to a medical device, such as a pacemaker, and whose distal end is to be affixed in a ventricle or atrium of the heart, can, after intravenous introduction into the heart, be passively or actively affixed to the heart wall in order to deliver electrical impulses to heart muscle, thereby causing it to contract, or sense the heart's intrinsic activity in order to control the pacemaker's operating cycle. In passive fixing of the electrode cable, the distal end is usually equipped with small fins or tines to facilitate anchoring this end in the heart wall without penetrating same.
In order to achieve rapid and positive fixing of the distal end of the electrode to the heart wall in implantation of the electrode cable, e.g. when the end of the cable is to have a J shape and press against an atrial wall, active fixation of the cable end to the atrial wall is preferred. For this purpose, the end of the electrode is provided with an anchoring element which can be screwed into wall tissue during implantation. The procedure can be monitored with fluoroscopy to ensure that the cable end is correctly positioned.
A commonly used anchoring element for this purpose has a helical means with a pointed tip. Electrode ends of this kind require active screwing of the anchoring means into the heart wall. In instances in which the helical anchoring element can freely rotate on the end of the electrode cable, the helical screw can be rotated with the aid of a stylet inserted from the proximal end of the electrode cable and engage a polygonal recess in the proximal end of the helical element thereby enabling this helical element to be rotated and affixed to the heart wall with the end of the electrode pressing against that wall.
In order to prevent the pointed end of the helical element from coming into contact with and damaging the walls of veins and the heart during the electrode cable's implantation, the aforementioned freely rotating helical element can be initially retracted into a protective recess at the end of the electrode cable and deployed, with the aid of the stylet, only after the end of the cable has reached the desired fixation site and just before the helical element is screwed in.
In another type of anchoring means for active affixing of the end of the electrode to the heart wall, a non-rotating helical element is attached to the distal end of the electrode and projects freely from same. In this instance the helical element must be provided with some kind of protector to keep the tip of the helical element from damaging the wall of veins and the heart during the electrode cable's implantation. The entire electrode cable, including its sheath, must then be rotated in order to drive the helical element into the heart wall.
Different solutions have been proposed for preventing such fixed, projecting helical element from causing damage during introduction. For example, U.S. Pat. No. 4,876,109 describes a body, covering the helical element, which dissolves in body fluid within a few minutes, whereupon the helical element can be screwed into the heart wall.
Another proposal is shown in U.S. Pat. No. 3,974,834 in which a compressible, bellows-like sleeve on the distal end of the electrode cable protects the helical element during intravenous introduction of cable into the heart and is compressed when pressed against the heart wall, enabling the tip of the helical element to gain a footing before being screwed into the heart wall.
U.S. Pat. No. 5,447,533 shows an active electrode affixing arrangement in which a helical element is kept protectively retracted inside a recess in the distal end of the electrode cable to keep the tip of the helical element from damaging the venous wall during intravenous introduction of the electrode cable introduction into the heart. A medication-dispensing element is arranged to slide coaxially inside the helical element after the helical element has been screwed into the heart wall, towards the heart wall in order to deliver medication to same, e.g. an anti-inflammatory agent.